Allow the dounmount() to proceed even for doomed coveredvp.

In dounmount(), before or while vn_lock(coveredvp) is called, coveredvp
vnode may be VI_DOOMED due to one of the following:
- other thread finished unmount and vput()ed it, and vnode was chosen
  for recycling, while vn_lock() slept;
- forced unmount of the coveredvp->v_mount fs.
In the first case, next check for changed v_mountedhere or mnt_gen counter
would be successfull. In the second case, the unmount shall be allowed.

Submitted by:	sobomax
MFC after:	2 weeks

1 files changed, 1 insertions, 3 deletions

diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 40fd361..e545a25 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1168,14 +1168,12 @@ dounmount(mp, flags, td)
 		mnt_gen_r = mp->mnt_gen;
 		VI_LOCK(coveredvp);
 		vholdl(coveredvp);
-		error = vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK, td);
+		vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK | LK_RETRY, td);
 		vdrop(coveredvp);
 		/*
 		 * Check for mp being unmounted while waiting for the
 		 * covered vnode lock.
 		 */
-		if (error)
-			return (error);
 		if (coveredvp->v_mountedhere != mp ||
 		    coveredvp->v_mountedhere->mnt_gen != mnt_gen_r) {
 			VOP_UNLOCK(coveredvp, 0, td);